Chords ii7, iii7 and vi7 in major keys and iv7 in minor keys (along with i7 in the natural minor) are known as minor sevenths - both the third and the seventh above the root are minor intervals. In the major, ii7 often forms part of the cadential progression ii-V-I and a perfect cadence is sometimes reached with even longer chains of non-dominant sevenths - each resovling onto the chord the fifth below (see chains of fifths).